Why wont my car tick over I have replaced the.

RAYRAY1.

1999 FORD FOCUS

Why wont my car tick over I have replaced the starter motor and it still wont tick over. Also every now and then my speed counter tells me am not moving but I am doing 70mph and then it works properly after a few mins and also mt battery light flashed a few days ago is this a faulty wire or do I just need a new battery